1. Field of the Invention
The present invention relates to a process for preparing polyester elastomers having rubbery elasticities including excellent low-temperature resistance and recovery.
2. Description of the Prior Art
Recently, a thermoplastic elastomer having a so-called micro-phase separation structure, i.e. having a soft segment which realizes a soft, rubbery elasticity and a hard segment which realizes a hard, aggregated domain by forming physical crosslinkings according to a mutual action such as crystallization or hydrogen bonding in the molecular chain, has attracted attention, since the following facts have been found: the thermoplastic elastomer can be molded by a process generally employed for molding thermoplastic resins; substances widely ranging from a rubbery substance to a plastic substance can be obtained easily by suitably selecting the soft segment-forming and the hard segment-forming components; and the micro-phase separation structure of this material has special properties such as antithrombotic activities, membrane separation functions and adhesiveness.
The soft segment-forming components of the thermoplastic elastomers preferred from the viewpoint of low-temperature properties are polyoxyalkylenediols such as polyoxyethylene glycol, poly(oxy-1,2-propylene)glycol, polytetramethylene glycol, block or random copolymer of ethylene oxide and propylene oxide, and block or random compolymer of ethylene oxide and tetrahydrofuran. Among them, polyoxytetramethylene glycol is recommended from the viewpoint of its thermal resistance, water resistance, low-temperature properties, elastic recovery and mechanical strength. This compound is now in use as the soft segment-forming component for polyester elastomers.
However, when the polyoxytetramethylene glycol having a molecular weight exceeding a certain value is used, crystallization is caused in the soft segment due to its linear structure and, therefore, the properties thereof such as low-temperature properties and elastic recovery are not always satisfactory.